1. Field of the Invention
The invention relates to a technical field of light emitting diode (LED) power equipment, and more particularly to an adaptive LED dimming driving circuit supporting TRI-electrode AC switch (TRIAC) that flexibly compensates outputted driving electricity by means of detecting the inputted electricity ripple voltage difference real-time so that the work efficiency of whole circuit can be improved, and the twinkling problem on LEDs can also be prevented.
2. Description of the Related Art
Currently, the driving circuit of an LED lamp is to linearly regulate the LED brightness and is accomplished by means of switching an input voltage conduction angle through a TRIAC. To retain the stable power for improving the illumination quality, a constant current architecture is usually adopted and allows an LED to cascade a transistor and a sensing resistor. A driving current ILED flowing through the LED is sensed by the sensing resistor so as to form a voltage drop at two ends. Afterward a high level switching signal or a low level switching signal is outputted to the transistor after utilizing a comparator to compare the voltage drop so that the transistor is conducted or cut off to properly regulate the duty ratio of a pulse width modulation (PWM) signal. Accordingly, the magnitude of the outputted driving voltage can be controlled by conducting cycle length through the PWM signal, thereby affecting the magnitude of driving current ILED and light emitting brightness of the LED.
As shown in FIG. 1, while inputting voltage 120V, a conventional linear dimming driving circuit is actually measured to obtain 7.3 watt, 69.1% whole circuit efficiency and 0.908 power factor for the LED. It should be noted that the driving circuit architecture is simple and can be obtained with high power factor. However, the figure also shows that although the brightness of the LED has been regulated to the maximum, the power consumption watt of the LED is still increased in accordance with the raising of inputted voltages. Consequently, the energy conversion efficiency will be seriously damaged. On the other hand, the LED may be affected by the fabrication process to have different physical properties so as to show different resistances such that the flowing current of each string of LEDs or an across voltage at two ends is not identical. Accordingly, the foregoing dimming method may affect the whole circuit efficiency due to different changes of voltages and current, and the problem of inaccurately dimming effect may occur. Moreover, the circuit architecture utilizing the transformer or the inductor to realize the switching of duty ratio of PWM signals has problems of electromagnetic interference (EMI) and twinkling. At this time, if safety components are increased, the work efficiency of the whole circuit is reduced to cause non-practicality. Additional circuits are increased to supply TRIAC reference working current. It may still work due to retaining current to form high idle work consumption since the LED is regulated to reach the maximum light emitting brightness.
Accordingly, improving the conventional dimming circuit architecture to properly regulate TRIAC retaining current through a simple detection circuit and effectively reducing idle work consumption while allowing the driving current ILED to retain at constant state are an important issue. Moreover, responding with LED's physical property, the high voltage compensation of inputted voltage is realized by utilizing a simple circuit architecture so that the whole circuit quality can be actually increased, and the light emitting power of the LED can be effectively improved. The foregoing situation will be also further discussed.